This invention relates to coiled tubing injection equipment used in the oil and gas industry and more particularly to gripper blocks used in coiled tubing injectors. As is well known in the art, coiled tubing injectors are typically used to move coiled tubing into and out of oil and gas wellbores.
Reeled or coiled tubing has been run into wells for many years for performing certain downhole operations, including but not limited to completions, washing, circulating, production, production enhancement, cementing, inspecting and logging. There are a number of patents issued on coiled tubing injectors and related equipment. Such injectors typically use a pair of opposed endless gripper chains mounted in a common plane. The gripper chains are normally made up of links, rollers and gripper blocks. Opposed gripper blocks on the endless chains opposingly engage the tubing so as to firmly grasp the tubing in such a way that the gripper blocks will force the tubing into or out of a wellbore when the gripper chains are driven. On setting the gripper chains into motion and upon each opposing pair of gripper blocks releasing their hold on the tubing, another pair of opposed gripper blocks grippingly engage the tubing and the cycle continues until a desired amount of tubing has been inserted or withdrawn from the wellbore, or until the gripper chains are no longer driven.
A variety of gripper blocks have been developed to improve the performance of coiled tubing injector units. Such improvements include designs directed to increasing the load carrying capability of the gripper block, eliminating or limiting scarring and distortion of the tubing caused by gripper block engagement, providing the ability to accommodate differing tubing diameters without having to change gripper blocks, reducing the weight of gripper blocks and reducing the manufacturing costs of gripper blocks. Such prior art gripper blocks are disclosed in U.S. Pat. No. 5,094,340 to Avakov, issued Mar. 10, 1992, and U.S. Pat. No. 5,853,118 to Avakov issued Dec. 29, 1998, both assigned to the assignee of the present invention, the details of both of which are incorporated herein by reference.
The gripper blocks described in the aforementioned patents have great utility in that they will accommodate different tubing diameters without having to change gripper blocks. As depicted in FIG. 1, a prior art gripper block 2 has opposite sides 4, opposite ends 6 and 8 positioned along an imaginary longitudinal axis, and a gripping region 10 running parallel to the longitudinal axis for gripping a section of continuous tubing, tube or other article that is to be injected or withdrawn, or otherwise have a force imparted thereon. End 8 has a wedge-shaped tongue 12 extending therefrom. End 6 has ears 9 extending therefrom defining recessed region 11 therebetween. A single borehole, or pin hole 14 extends through the gripper block body 2.
Tubing gripping region 10 located on the upper portion of block 2 includes a pair of angled or sloped gripping surfaces 16 which diverge away from a base area to form a generally V-shaped profile when viewed from either end of block 2. Surfaces 16 and 18 comprise alternating ridges and grooves 20 and 22, respectively, configured to resemble acme-type threads.
The prior art gripper block described in FIG. 1 can be effectively utilized to move tubing or other elongated objects of various diameters in and out of a wellbore and has enjoyed commercial success. Typically, the coiled tubing utilized with such prior art gripper blocks is a steel coiled tubing which can be utilized to perform a wide variety of operations in a wellbore. However, it has been found that using such gripper blocks to move composite coiled tubing is not as efficient as desired, since the sloped planar surfaces in the gripping region often cause damage to composite coiled tubing.
Composite coiled tubing is lighter than steel coiled tubing and is easier to force into wells that deviate from the vertical, including horizontal wells. Thus, there are times when it is preferable to use a composite coiled tubing to perform a desired operation, and other times when it may be preferable to use a steel coiled tubing. Although the prior art gripper blocks described herein work adequately with steel coiled tubing, they are not effective for use with composite coiled tubing. If it is desired to perform an operation with composite coiled tubing, a different gripper block must be used. The injector unit must therefore be disassembled, and gripper blocks compatible with composite tubing must be installed. If it is later desired to utilize steel coiled tubing, the composite compatible gripper blocks must be replaced with blocks designed to move steel coiled tubing.
Thus there is a need for a gripper block which has a gripping surface that is capable of accommodating varying sizes of coiled tubing and that is also capable of accommodating different material types such as steel and composite coiled tubing.